1. Field of the Invention
The invention relates to electric power steering systems. Specifically, the invention relates to disconnecting power from a motor of an electric power steering system.
2. Description of the Related Art
Modern vehicles typically offer power steering systems to aid the driver in turning the wheels of the vehicle via the steering wheel. This assistance is most often needed at slow or stopped vehicle speeds. Conversely, very little assistance is needed when the vehicle is traveling at higher speeds.
Conventional power steering is accomplished using hydraulic mechanisms. However, electric power steering systems have recently become more commonplace. Electric power steering systems include an electric motor operatively connected to the wheels of the vehicle to provide assist when the driver turns the steering wheel. The amount of electrical power provided to the electric motor is typically varied based on a number of factors, including, but not limited to, the speed of the vehicle. A control diagram for such a prior art system can be seen in FIG. 1.
In case of a fault in the electric power steering systems, it is often necessary and prudent to disconnect all electric power from the electric motor, thus resulting in manual steering of the vehicle. This disconnection of power from the electric motor in the prior art is accomplished by one or more relays, as can be seen in prior art FIGS. 1 and 2. More specifically, as shown in FIG. 2, a disconnect relay is electrically connected between a power input and at least one power device.
Unfortunately, this prior art system has numerous shortcomings. For instance, the resistance from the relay contacts is undesirable as they provide a source of power loss in the system. Furthermore, the electromechanical relays are physically large and expensive due to the large amount of current they need to carry, as well as often being unreliable. Moreover, multiple (redundant) battery measurement is required on both sides of the relay to ensure proper operation.
The present invention attempts to solve these and other problems of prior art electric power steering systems.